Sucrose treated carbon nanotube and graphene yarns and sheets

ABSTRACT

Consolidated carbon nanotube or graphene yarns and woven sheets are consolidated through the formation of a carbon hinder formed from the dehydration of sucrose. The resulting materials, on a macro-scale are lightweight and of a high specific modulus and/or strength. Sucrose is relatively inexpensive and readily available, and the process is therefore cost-effective.

CROSS-REFERENCE TO RELATED PATENT APPLICATION(S)

This patent application is a divisional application of and claims thebenefit of and priority to U.S. patent application Ser. No. 14/206,292,filed on Mar. 12, 2014, now U.S. Pat. No. 9,695,531, which claims thebenefit of and priority to U.S. Provisional Patent Application No.61/786,825, filed on Mar. 15, 2013, the contents of both applicationsare hereby incorporated by reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein was made in the performance of work undera NASA contract and by employees of the United States Government and issubject to the provisions of Public Law 96-517 (35 U.S.C. § 202) and maybe manufactured and used by or for the Government for governmentalpurposes without the payment of any royalties thereon or therefore. Inaccordance with 35 U.S.C. § 202, the contractor elected not to retaintitle.

FIELD OF THE INVENTION

The present invention relates to a method of treating carbon nanotube(s)or graphene yarn(s) and sheet(s) to improve the transport and mechanicalproperties thereof, and specifically to a process of treating thematerial with sucrose to lock the carbon nanotubes or graphene sheets inalignment with one another.

BACKGROUND OF THE INVENTION

Various aerospace and terrestrial applications require lightweightmaterials with very high mechanical properties, particularly specificmodulus and strength. Carbon nanotubes and graphene sheets have beenfound to be such materials. In addition, they have been found to haveexcellent electrical and thermal transport properties. Howevertranslating the excellent properties, particularly mechanical andthermal transport, at the nanoscale level to bulk materials has provento be a difficult challenge. In order for the nanotubes to be used inapplications, they must be spun into yarn(s), sheet(s), and othermacroscopic forms introducing relatively weak tube-to-tube andinter-bundle bonds. Also, the nanotubes tend to be entangled, and theytherefore do not all contribute in load bearing. Weak coupling at tubeand bundle interfaces also leads to mechanical and thermal transportthat are much lower than would be expected from the carbon nanotube orgraphene properties.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention is a method of treating carbonnanotube/graphene yarn, sheet, tape or other macroscopic form. Thematerial is soaked in a sucrose solution, and the sucrose solution isthen chemically or thermally dehydrated to form a carbon binder. Thesoaking and subsequent reduction can be repeated numerous times toobtain the desired sucrose penetration and to form a binder of thedesired thickness. Stretching of the carbon nanotube/graphene materialduring the sucrose infusion and dehydration process leads to locking inof alignment as the binder forms. Such alignment of the carbonnanotubes/graphene sheets leads to large enhancements of the mechanicalproperties as more of the nanotubes or graphene sheets contribute toload bearing. The strong tube-to-tube and bundle bonds introduced by thecarbon binder also serve to enhance the overall mechanical and thermaltransport properties of the material as these bonds form conduits forphonons.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing a process according to one aspect of thepresent invention;

FIG. 2 is a graph showing mechanical properties of carbon nanotube yarnsthat has been treated with either a sucrose/ethanol mixture or asucrose/water mixture;

FIG. 3 is a graph showing mechanical properties of carbon nanotube yarnstreated with a sucrose/ethanol/water mixture;

FIG. 4 is a graph showing mechanical properties of carbon nanotube yarnsthat have been treated with a sucrose mixture over several treatmentcycles.

DETAILED DESCRIPTION OF EMBODIMENTS

For purposes of description herein, it is to be understood that theinvention may assume various alternative step sequences, except whereexpressly specified to the contrary. It is also to be understood thatthe specific devices and processes illustrated in the attached drawings,and described in the following specification, are simply exemplaryembodiments of the inventive concepts defined in the appended claims.Hence, specific dimensions and other physical characteristics relatingto the embodiments disclosed herein are not to be considered aslimiting, unless the claims expressly state otherwise.

The present invention relates to a process for treating carbonnanotube(s) and graphene yarn(s) and sheet(s) with sucrose to improvethe mechanical properties of the tube(s), sheet(s), or yarn(s). Anycombination of tube(s), sheet(s), yarn(s) can be simultaneously treated.With reference to FIG. 1, carbon material in the form of nanotube orgraphene yarn or sheet is initially provided at step 1. The carbonmaterial generally comprises a plurality of microscopic structures suchas nanotubes, graphene sheets, or any combinations thereof that areinterconnected to form a macroscopic yarn or sheet material. The sheetmaterial can be woven or unwoven. Prior to treatment, the carbonmaterial has a first specific modulus. At step 2, the carbon nanotube(s)or graphene sheet(s) are aligned. Alignment is accomplished bystretching the carbon material by applying a force to the material. Asucrose solution is then applied to the carbon material at step 3. Thesucrose solution can be applied by soaking the carbon material, such ascarbon yarn or sheet material, in a liquid sucrose solution. The liquidsucrose solution can comprise sucrose and a solvent, wherein the solventcan comprise one or more of water, ethanol, and water/ethanol mixtures.In one embodiment, the liquid sucrose solution is sucrose dissolved inwater and ethanol. It will be recognized that various other solvents mayalso be utilized to dissolve the sucrose.

After the sucrose solution is applied, the carbon material is thendried, wherein water is removed from the solvent used in the sucrosesolution, and the sucrose then dehydrated (dry process) or dehydrationof the sucrose can be done without the drying step (wet process), asshown in step 4. For the purposes of this application, dehydration isdefined as the removal of hydroxyl groups from sucrose to form theamorphous carbon. The dehydration is carried out with acid. In someembodiments, the acid used is sulfuric acid. In some embodiments theacid can be concentrated sulfuric acid. Various chemical dehydrationagents including, for example concentrated sulphuric acid (H₅SO₄) (aswell as heat treatment), can be used to treat and dehydrate the sucrose.After dehydration, the carbon material can be washed to remove anyunreacted sucrose or dehydration agent(s), step 5. Applying anddehydrating the sucrose solution while stretching the material (steps 2to 5) can be repeated numerous times to form a binder of the desiredthickness (arrows 6 and 7). In some embodiments, the desired thicknessof the binder is a thickness that yields less than about 60% by weightof the resulting nanocomposite. In other embodiments, the binderthickness is less than about 50% by weight, less than about 40% byweight, less than about 30% by weight, less than about 20% by weight,less than about 10% by weight, less than about 5% by weight or less thanabout 1% by weight of the resulting nanocomposite. The material ispreferably stretched in the same direction during the repeated soakingin the sucrose solution and dehydrating of the sucrose.

The process of applying the sucrose solution and dehydrating the sucroseforms a binder that locks the individual carbon nanotubes or graphenesheets and bundles of graphene sheets to one another. In variousembodiments the carbon material can be made of nanotube(s), graphenesheet(s), bundles of graphene sheets or any combination of theforegoing. Stretching of the carbon material during the process ofapplying and dehydrating the sucrose aligns the individual carbonnanotubes or graphene sheets relative to one another, and the sucrosebinder locks the microscopic structures in alignment. Such alignment ofthe carbon nanotubes or graphene sheets in the final material leads tolarge enhancements of the mechanical properties (e.g. specific modulus)as more of the carbon nanotubes or graphene sheets contribute to loadbearing. The interlocking binder improves the interaction of the tubesand bundles, limiting slippage and thus enhancing load carryingcapacity. Additionally, the bridges formed by the binder serve toenhance the phonon transport properties, in some embodiments thealignment of the microstructures is 100% in the load direction. In otherembodiments the microstructure alignment can be about 90%, about 80%,about 70%, about 60%, about 50% or about 40% in the load direction.

Referring again to FIG. 1, after drying the sucrose solution anddehydrating the remaining sucrose, the carbon material can be washed andsubject to further processing. For example, the carbon material can beannealed or used as a platform for further chemical treatment of theyarns or sheets.

Various carbon composite structures can be formed utilizing the treatedcarbon material such as treated carbon yarns or sheets. For example, thetreated carbon material can be dispersed in a matrix material (e.g.polymer resin) to form a carbon fiber structural material. The carbonfiber structural material can be a rigid composite structure. Numerousaerospace applications require lightweight structural materials withhigh specific modulus and strength. Examples of applications include,but are not limited to, structural materials for aerospace vehicles,materials for lightweight, mechanically robust consumer devices, andmaterials for space habitats.

Testing of the carbon yarn treated according to the present inventionhas shown a dramatic increase in mechanical properties. FIG. 2 is agraph showing the mechanical properties of carbon nanotube (“CNT”) yarnstreated with a sucrose and ethanol mixture and of carbon nanotube(“CNT”) yarns treated with a sucrose and water mixture. The mixtures ofFIG. 2 were a saturated solution of sucrose. As shown in FIG. 2, themechanical properties (modulus) of the yarns increase significantlyafter treatment with the sucrose and ethanol or the sucrose and watermixtures.

FIG. 3 is a graph showing the mechanical properties of carbon nanotube(“CNT”) yarns that have been treated with sucrose dissolved in anethanol/water mixture. Again, the mechanical properties (modulus) of theyarns increase significantly after treatment with the sucrose withethanol/water mixtures. From FIG. 4(3), cycle 1 added ˜0.2 g/m ofamorphous carbon to the yarn. Cycle 3 added a total of 0.5 g/m ofamorphous carbon to the untreated yarn. These numbers were calculatedfrom the tex values shown on the graph caption where tex is defined asg/m length of the CNT yarn.

FIG. 3 also shows the results of both a wet process and a dry processutilizing a concentrated (98%) H₂SO₄ solution. Drying requires heatingto 110° C. to remove the water. Dehydration is carried out by dippingthe dry treated material in concentrated sulfuric acid until thereaction is complete—no more fumes are formed so all the sucrose hasreacted.

FIG. 4 is a graph showing the mechanical properties of CNT yarns treatedover several cycles. Control yarns have no treatment. Sucrose yarns arealways treated with a solution of sucrose so it would be sucrosemixture. Mixture concentrations are always saturated sugar solutions.Sucrose 1 and sucrose 4 are treated with the same sucrose mixture andonly differ from each other by the number of sucrose mixture treatmentcycles.

The carbon obtained from the dehydration of the sucrose serves to bindthe CNTs/CNT bundles in the sheet or yarn to lock in alignment andenable better load transfer between the tubes and/or bundles leading tomaterials with greatly enhanced mechanical properties as shown in FIGS.2-4. FIGS. 2-4 show that a greater than 30% increase in tensileproperties was realized for non-optimum starting materials.

It is to be understood that variations and modifications can be made onthe aforementioned structure without departing from the concepts of thepresent invention, and further it is to be understood that such conceptsare intended to be covered by the following claims unless these claimsby their language expressly state otherwise.

All cited patents, patent applications, and other references areincorporated herein by reference in their entirety. However, if a termin the present application contradicts or conflicts with a term in theincorporated reference, the term from the present application takesprecedence over the conflicting term from the incorporated reference.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other. Each rangedisclosed herein constitutes a disclosure of any point or sub-rangelying within the disclosed range.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. “Or” means “and/or.” As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.As also used herein, the term “combinations thereof” includescombinations having at least one of the associated listed items, whereinthe combination can further include additional, like non-listed items.Further, the terms “first,” “second,” and the like herein do not denoteany order, quantity, or importance, hut rather are used to distinguishone element from another. The modifier “about” used in connection with aquantity is inclusive of the stated value and has the meaning dictatedby the context (e.g., it includes the degree of error associated withmeasurement of the particular quantity).

Reference throughout the specification to “another embodiment”, “anembodiment”, “some embodiments”, and so forth, means that a particularelement (e.g., feature, structure, and/or characteristic) described inconnection with the embodiment is included in at least one embodimentdescribed herein, and can or cannot be present in other embodiments. Inaddition, it is to be understood that the described elements can becombined in any suitable manner in the various embodiments and are notlimited to the specific combination in which they are discussed.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and can include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

The invention claimed is:
 1. A carbon material, comprising: a pluralityof microscopic carbon structures that are interconnected to form a sheetor yarn, wherein 40 to 100 percent of the microscopic carbon structuresare at least partially aligned with one another; a dehydrated sucrosebinder formed by subjecting sucrose to a dehydration reaction, thedehydrated sucrose binder dispersed on at least some of the microscopiccarbon structures; wherein the dehydrated sucrose binder binds adjacentmicroscopic carbon structures together and maintains alignment of themicroscopic carbon structures.
 2. The carbon material of claim 1,wherein the microscopic carbon structures comprise carbon nanotubes. 3.The carbon material of claim 2, wherein the carbon nanotubes form amacroscopic sheet.
 4. The carbon material of claim 2, wherein the carbonnanotubes form a macroscopic yarn.
 5. The carbon material of claim 1,wherein the sheet is a woven material.
 6. A rigid composite structure,comprising: the carbon material of claim 1 and a rigid matrix material,wherein the carbon material is provided in the rigid matrix material toform the rigid composite structure.
 7. The rigid composite structure ofclaim 6, wherein the rigid matrix material comprises a polymer.